java - 单例和单元测试

Question

Effective Java 有以下关于单元测试单例的声明

Making a class a singleton can make it difficult to test its clients, as it’s impossible to substitute a mock implementation for a singleton unless it implements an interface that serves as its type.

谁能解释为什么会这样？

Answer 1

您可以使用反射来重置您的单例对象，以防止测试相互影响。

@Before
public void resetSingleton() throws SecurityException, NoSuchFieldException, IllegalArgumentException, IllegalAccessException {
   Field instance = MySingleton.class.getDeclaredField("instance");
   instance.setAccessible(true);
   instance.set(null, null);
}

引用:unit-testing-singletons